Surface treated steel sheet for use in a forming operation

ABSTRACT

Surface treated steel sheet for use in a forming operation having a layer of a higher alcohol material which is solid at room temperature and of which the major constituent is one or more substances selected from the group consisting of higher alcohols, and, beneath the former layer, a layer of a chemically treated coating film or a layer of coating film of one or more metals selected from the group consisting of Zn, Pb, Cd, Cu, Cr, Sn and Al.

Kushima et al.

SURFACE TREATED STEEL SHEET FOR USE IN A FORMING OPERATION Inventors: Hosei Kushima; Kanji Yahano, both of Himeji, Japan Assignee: Nippon Steel Corporation, Tokyo,

Japan Filed: July 26, 1971 Appl. No.: 164,797

Foreign Application Priority Data July 30, 1970 Japan 45/66762 References Cited UNITED STATES PATENTS 12/1953 Montgomery et a1 148/6.15 R

[ Oct. 16, 1973 3,046,165 7/1962 Halversen et al. 148/615 R 2,420,886 12/1942 Laffoon 148/624 2,773,623 12/1956 Schuster et al. 148/614 R 2,438,013 3/1948 2,359,095 9/ l 944 3,392,117 7/1968 2,686,355 8/1954 3,438,754 4/1969 Primary Examiner-Alfred L. Leavitt Assistant Examiner-Frank Frisenda AttorneyDavid Toren et al.

[ 5 7] ABSTRACT Surface treated steel sheet for use in a forming operation having a layer of a higher alcohol material which is solid at room temperature and of which the major constituent is one or more substances selected from the group consisting of higher alcohols, and, beneath the former layer, a layer of a chemically treated coating film or a layer of coating film of one or more metals selected from the group consisting of Zn, Pb, Cd, Cu, Cr, Sn and Al.

2 Claims, No Drawings SURFACE TREATED STEEL SHEET FOR USE IN A FORMING OPERATION This invention relates to a surface treated steel sheet for use in a forming operation, which can be easily lubricated and from which adhering matter can be readily detached.

As lubricants for steel sheet used in a press forming operation, oily lubricants in liquid or paste form have hitherto been used. Recently, however, attempts have been made to apply solid lubricants in which metallic soaps are the major constituent. These lubricants having metallic soap groups are advantageously applied as a preliminary lubricant to a surface treated steel sheet not only because of their better lubricating ability relative to that of oily lubricants but also because of the convenience with which the steel sheet can be handled after the application of the solid lubricants. On the other hand, as they are applied in the form of an aqueous solution, prolonged high temperature heating is required to dry the coating. This leads to the degraded producibility, accelerates aging of the steel sheet and deteriorates the quality of the steel, which also decreases the workability in the forming operation.

As a remedy to cover the drawbacks of the lubricants containing these metallic soaps, the present inventors have developed preliminarily lubrication treated steel sheets, the surface of which is coated first with a metal selected from the group consisting of zinc, copper and cadmium or an alloy thereof and further with a layer of a substance that is solid at room temperature and is composed higher carboxylic acids. A portion of these developments have been published in Patent Publication Sho 44-16774 and Sho 44-20217.

The surface coating material of which a higher carboxylic acid is the main constituent can be applied more easily and is better in lubricating action relative to the coating film of metallic soap. Further, since the said coating material does not require high temperature drying in the treatment, it does not accelerate the aging of the steel sheet and, hence, does not deteriorate the material of the steel sheet itself. However, the coating film can not be removed easily. More particularly, a longer time is required to remove the coating film in the alkali degreasing process than it does with a steel sheet on which anti-rusting oil is applied.

This is presumably due to the higher carboxylic acid which was chemically adsorbed firmly on the plated layer of Zn, Pb, Cd or Cu or the chemically treated coating film, both existing as the primary layer on the steel sheet. This is one of the drawbacks encountered during painting after the press molding process.

The composition for coating is required, on one hand, to have strong adsorptivity to produce a sufficient lubricating property on the surface, for example owing to polar groups contained in the moecules. On the other hand, however, there should be a limitation to the adsorptivity since easy removal of the coating film is also required after the molding process.

On the whole, compounds having a carboxyl group or groups, such as, higher carboxylic acids, which are chemically adsorbed firmly on a plated layer of Pb, Cd or Cu or on a thin layer of chemically treated coating film on the surface of a steel sheet, are not suitable to use for a surface lubricant when the property of easy removal is essential.

The present inventors have recently discovered, as a consequence of various investigations on this problem, that a steel sheet which is first coated with a certain film and then treated with a higher alcohol coating material, which is solid at ambient temperature, meets the requirement.

The higher alcohol application agent has only weak absorbing power to the surface of steel sheet, as is generally recognized, and therefore if a steel sheet, on which the agent has been applied directly on the surface, is treated by the molding process, the lubricating film thus formed can not follow the increase of area as a result of the molding process and may result in burning or bite of the surface. Therefore, the material has not been used as lubricating agent for the molding process.

The metal coatings of this invention to be applied on a steel sheet include the following ones:

1. A coating with a metal selected from the group consisting of Zn, Pb, Cu and Cd, and a coating with an alloy in which the main constituent is one or more metals mentioned above produced by ordinary electroplating; a coating with a metal mentionedabove produced by an ordinary molten metal plating method; and a metal coating with which the surface of the steel sheet is converted to an alloy containing iron as an ingredient by a thermal diffusion treatment of any coating mentioned above to form alloy from the metal and the base steel.

2. The chemically treated coating films to be applied to the steel sheet include a layer of hydrated oxide which was obtained by applying anhydrous chromic acid or a phosphate or a mixture thereof in the form of an aqueous solution and a layer of metallic oxide which was deposited from an aqueous solution of chromate, phosphate or a mixture thereof by making the solution contact with the surface of the steel sheet in the presence of chemical reductant or with the combined use of electrolytical cathodic reduction or further a baking treatment.

The steel sheet of this invention is produced by applying on the above mentioned coating films a higher alcohol material which is solid at room temperature and of which the main constituent is one or more substances selected from the group consisting of the higher alcohols described below.

For the higher alcohol materials to be applied, those alcohols containing at least 12 carbon atoms in the molecule which becomes solid after being applied at the room temperature are preferred. They include, for example, dodecanol, tetradecanol, hexadecanol and octadecanol.

Admixing a rust preventure agent, a coloring material and a filler to the higher alcohol material to such an extent as not to alter the fundamental properties of the material does notspoil the effect of the steel sheet of this invention.

The ways in whichthe higher alcohol materials which are solid at the room temperature are applied to the surface of steel sheets include applying in liquid form, either made molten by heating or in the form of a solution in an organic solvent, with rollers, spray, brush or by dipping or streaming, onto the surface of the steel sheet followed by heating with an infrared light or hot air to fuse the material and form a uniform layer on the surface.

In applying a metal coating of Zn, Pb, Cd or Cu on the steel sheet base, uniform application of the said higher alcohol materials and excellent workability in the forming operation can be attained for the applied amount more than 250 mg/m when one of the metals is applied along and more than 250 mg/m as the total amount of the said metals when an alloy coating is applied. As the amount of the metal coating is increased further, the lubrication effect of the higher alcohol materials is improved even more until the total amount of the metal coating reaches 2500 mglrn and the lubrication effect remains constant for an amount of metal coating over 2500 mg/m. Therefore, the amount of the metal coating of this invention should be preferably more than 250 mglm The amount of the chemically treated coating film to be formed either directly on the surface of steel sheet or on the metal coating of the above mentioned metals and Cr, Sn and Al should be preferably more than 300 ing/m when a chemically treated coating film of hydrous oxide or hydrated metal oxide is formed from an aqueous solution of phosphate. For an amount less than 300 mglm not only the coating film itself but-also the higher alcohol materials applied on it become nonuniform, which means the lowered ability in lubrication. Thus, an amount larger than 300 mg/m is desired.

On the other hand, when the chemically treated coating film of hydrous oxide or hydrated metal oxide is formed from an aqueous solution of chromate, an amount larger than 50 mg/m is desired. The lubricating ability is increased with an increase in the amount of coating film, but for an amount less than 50 mglm sufficient lubricating ability is not attained for practical purposes.

In the case where an aqueous solution containing both anhydrous chromic acid and phosphate is applied, an amount of the coating film larger than 50 mg/m the same as with the chrom ate treatment, is desired.

The higher alcohol material that is solid at the room temperature produces an appreciable effect even when it is applied in a small amount, but a remarkable effect when applied in an amount larger than 50 mg/m. The effect on the lubricating ability is increased with an increase of the applied amount, but the upper limit may be set to 5 mg/m in practical application to the steel sheet of this invention, considering the accumulated adhesion of the material to rollers and the mold for forming, transfer of the adhering material to the steel sheet, time required to remove it and the contamination of wash liquid. 1

The steel sheets of this invention include, in addition to the steel sheets on which the surface treatment of this invention is applied on the whole surface of both sides, those steel sheets on which the surface treatment is applied on the whole surface of a single side or on a part of a single or both sides. The latter treatment may be suitable depending on the forming operation.

The steel sheets of this invention are produced from the following three stages of operation: production of the steel sheet (non-lated), application of the specified coating film on the steel sheets and application of the higher alcohol materials. These three stages of operation are not necessarily performed in a factory, but the higher alcohol material may be applied, for example, in the blanking line or immediately before pressing in the pressing operation.

A steel sheet, as well as a cut sheet therefrom, which is produced in the way described above belongs to the present invention.

Advantages of the steel sheets of this invention will be described as follows:

1. Easy removal of the preliminary lubricant The preliminary lubricant can be easily removed with an alkaline degreasing agent or an organic solvent. The adhesive power of the higher alcohol material to the specified coating film of this invention is so weak as not to cause troubles in the forming operation in contrast to the corresponding material of carboxylic acid, and the former can be removed more easily than the latter. In addition, the small amount of the former material to be applied reduces contamination of the remover solution.

2. Excellent rust preventing ability Since the surface of the steel sheets is covered by the coating layer consisting of the specified coating film and the higher alcohol material, the surface is effectively protected from rust formation, and therefore application of oil for rust prevention is not required while the higher alcohol material exists on the surface.

3. In contrast to the difficultly drying water-soluble lubricants such as ordinary metallic soap lubricants, the higher alcohol material to be applied can be made molten by heating or may be applied on the surface of steel sheet in the form of a solution in an organic solvent, the material dries easily and a short time heating suffices if necessary, so that deterioration of the steel sheet does not occur and high producibility can be achieved.

4. The steel sheets of this invention on which the specified coating of chemically treated film is applied can be subjected to removal of the higher alcohol material after the forming operation and then to painting without treating the base surface, so that the producibility and the cost can be improved.

5. In the steelsheets of this invention on which the specified metal coating is applied, the higher alcohol material is removed after the forming operation is completed and then the metal coating of zinc or cadmium is finally removed by acid treatment. in the acid treatment, the metal coating of zinc or cadmium is dissolved in the acid solution acting as electrolytical anode against the steel base. As a result, the finally exposed surface of the steel base is extremely acitve as it is when treated cathodically with an acid solution, and therefore it forms a very good base for permanent plating. When the steel sheets of this invention are employed for such use, thin coating films of zinc or cadmium are preferred for economy and easy removal, that is, the total amount of zinc and cadmium in the film is 250 2500 mg/m". These coating films are also useful as preliminary coating films on which to form a uniform layer of a chemically treated coating of phosphate.

6. No difference from untreated steel sheets in weldability.

The steel sheet of this invention shows no difference from untreated uncoated steel sheets with respect to welding strength, and mars and stains by a welding machine.

7. Excellent workability in forming operation Although the lubrication effect of coating films of higher carboxylic acids is generally recognized as is published in Patent Publication Sho 44-467 74 and Sho 44-20217, the lubrication effect of the coating film of higher alcohol materials is no less excellent, so that a further application of a lubricating oil is not required. This leads to improved workability in the press forming operation and lowers the rejection rate.

8. Since the surface of the steel sheet of this invention is solid at room temperature, it is not sticky and does not become dirty. Due to the small amount of the higher alcohol material to be applied, the material does not drift or flow and does not transfer to another sheet when some sheets are piled. Thus, handling of the sheets is easier than of steel sheets to which rust preventing oil is applied.

EXAMPLE 1 Various coating materials and preliminary lubrication treatments relating to this invention as shown in Table l were applied on cold rolled rimmed steel sheets with a thickness of 0.8 mm, and the press forming test was conducted. Results are shown in Table 2.

As is evident in Table l and 2, the steel sheets of this invention were more easily workable in the forming operation than those of the conventional art and of comparison runs under any surface treatment condition,

5 since CCV the was lower by more than 0.8 mm and ErV was higher by approximately more than 1 mm.

EXAMPLE 2 The chemically treated coating films as described in parison purposes, commercial press oil was applied as examples of previous treatments. The final products were compared with respect to the workability. Results thereof are shown in Table 4.

' TABLE 1 p Coating to steel base Higher alcohol or lubricating oil Num- Amount Amount ber Material Method of application (gJnfl) Material (g. lmfl) This invention Phosphate 0- 5 Hexadecanol 0. 3 Conventional." .d0 0. 5 Commercial press oil 6 Thi i entio 0. 5 Hexadecanol 0.3 Conventional 0. 5 Commercial press oil. 6 This i ention 5 Hexadecanol 0. 3 Conventional. 5 Commercial press oil 6 This inventio 5 Hexadecanol 0. 3 Conventional 5 Commercial press oil 6 This invention.. 5 Hexadecanol 0. 3 5 Commercial press 6 5 Hexadecanol 0. 3 5 Commercial press 0il 6 6. 5-3. 5 Hexadeeanol 0. 3 6. 5-3. 5 Commercial press oil. 6 5. 5-4. 5 Hexadecanol 0. 3 5. 5-4. 5 Commercial press oil. 6 100 Hexadecanol 0. 3 100 Commercial press oil 6 80-20 Hexadecanol 0. 3 .do..- 80-20 Commercial press oil 6 Molten zinc plating plus thermal difiusion- 50-6 Hexadecanol 0. 3 do 50-6 Commercialpress oil 6 Electroplating plus spraying 5-1 Hexadecanol 0. 3 d 5-1 Commercial press oil 6 5-0. 5 Hexadecanol 0. 3 5-0. 5 Commercial press oi 6 No treatment ..do 6 do do Hexadecanol 0. 3 Zine Electroplatmg 5 Vaseline 5 REMARKS.PI8S8H1ZI Present invention; Conventional: Conventional treatment; Comparison: For comparison.

CCV ErV 0 CV ErV N0 (mm.) (mm.) N0 (mm (mm.)

Present 1 37. 0 12. 2 15 36. 7 12. 4 Conventional. 2 38.1 11.0 16 37. 9 11.6 Present 3 36. 8 12. 5 17 37. 2 l2. 0 Conventional... 4 38. 2 11. 2 18 38. 0 10. J 5 36. 5 12. 3 Present 19 36. 1 l2. 4

6 37. 6 11. 5 Conventional 20 37. 3 11. 0

7 36. 3 12. 4 Present 21 37. 0 12. 2

8 37. 4 l1. 6 Conventional 22 37. 8 11. 2

9 36. 4 12. 2 Present 23 36. 7 12. 0

10 37. 2 11. 3 Conventional 2 37. 8 10. 8

11 36. 6 12. 3 Present 25 36. 3 12. 9

12 38. 1 11. 2 Conventional 26 37. 5 11. 8

13 36. 4 12. 6 Conventional 27 37. 9 11. 3

Conventional 14 37. 5 l1. 6 28 37. 6 11. 1 29 38. 2 10. 7

diameter shoulder, flange restricted.

TABLE 3 Applied higher Plating Chemically treated coating illn'i nlcohol material Amount Amount (or lubri- Amount Material (gm/m?) Material Method of application (go/n13) eating oil) (gJinfl) Examples of this invention:

A No plating Hydrpus chromic Cathodic electrolysis in ii chromatc solution-.. 100 llexadccmiol. 0. 5

X1 8. B do Amixture of Cathodic electrolysis in a solution containing 30 --..do 0.5

hydrous phosphate and chromato. chronnc oxide and phosphorus oxide. 0 do Hydrous chromic Application of a solution containing phosphate 50 do 0.5

oxide. and anhydrous chromic acid. D do do Dipglllg in a. solution of chromate 50 ..do 0. E Zn 1 do Cat odic electrolysis in an aqueous solution of 100 .-.do 0.5

chromate. Examples of conventional treatment:

F Zn 1 Phosphate Spraying an aqueous solution of phosphate 500 do O. 5 G No plating Hydrous chrormc Cathodic electrolysis in an aqueous solution of 100 Commercial 5 oxide. chromate. press oil. H Zn 1 do Dipping in an aqueous solution of chromate do 5 W TABljEi l i Examples l Application of rust preventing oil V V 2 of cv v conven- .1 Application of machine oil No 120 3 (mm) m) tional A 36,7 11,2 treatment K Application of commercial press Examples oil 6 B 36.4 11.4 Examples L The same as in A on a chromate 0.2 of coating film this this M The same as in B etc. 1 I I C 37.0 11.0 invention N The same as in G etc. 0.2

D 36.9 11.1 Examples E for O The same as in H etc. I F 360 comparison Examples of Examples G 37.9 10.3 conventiena] :(fmvem The same as in 1 etc 2 treatment tional Q The same as in K etc. 6

treatment As seen in the table, the present invention exhibits TABLE 6 excellent workability in the forming operation.

workability Time required for removal EXAMPLE 3 Test (Sec) specimen Steel sheets of this invention were prepared by elec 40 CCV Erv spray Dipping tro-plating leas in the amount of l g/m on rimmed steel (mm) (mm) sheets of 0.8 mm thickness and treating the surface as gr asing greasing shown in Table 5. Tests of workability in the forming 22'; 32 i g8 operation and of removal of the treating agent were Examples conducted with specimens prepared from the steel C 5 10 1 18 sheets of this invention, the previous treatment and the invemion D 3642 125 lo 60 comparison runs. Results thereof are shown in Table 6. E 36.4 12.1 5 10 F 36.0 l2.6 10 60 TABLE 5 Examples G 37.0 12.4 10 120 for Treatment Amount applied comparison H 36.6 12.7 60 300 as non-volatile Examples l 38.5 l0.8 lo 60 matter (g/m) 0f A Application and in a COI'lVCnllO- J 38.7 l0.7 30 I20 perchloroeihylene solution of nail treattetradecanol 002 men! R 38.0 1 1.4 30 130 B Application and drying in a Examples L 36.9 12.2 ll) 30 perchloroethylene solution of of this ietradecanol and 40% invention M 36.3 12.6 30 on dodecanol 1 Examples N 37.2 12.1 30 120 Examples C Application and drying in a 0.2 for b of perchloroethylene solution of comparison 0 36.8 12.6 120 600 this hexadecanol Examples P 38.4 10.7 30 120 invenof iion D do. 1 60 conven- O 38.0 11.5 180 600 E Application and drying in a tiorial perchloroethylene solution of treatment octadecanol 0.2 F Application and drying in a perchloroethylene solution of CONDITIONS FOR TESTING 60% octadecanol and 40% hexadecanol i Test of workability: No lubricant was applied except Examples 0 Application and drying n a 0.2 as mentioned above for perchloroethylene solution -p f paimmc acid Test of time required for removal: 10 g/l of Perco- H cleaner No. 3645 EXAMPLE 4 Tests of workability were conducted with the steel sheets which were prepared by electroplating zinc in the amount of 10 g/m on cold rolled rimmed steel sheets of 0.8 mm thickness and then applying several different amounts of octadecanol in a perchloroethylene solution. Results are shown in Table 7.

TABLE 7 Amount of octadecanol CCV ErV applied (mg/m) (mm) (mm) 39.0 9.8 10 38.8 10.0 50 37.8 10.9 200 37.2 11.7 500 36.8 12.0 1000 36.5 12.2 5000 36.1 12.4

As is apparent in the table, the workability was improved with the increase of the applied amount, and this is especially remarkable for the amount larger than 50 mg/m EXAMPLE 5 Tests of workability were conducted with the steel sheets which were prepared by electrolytically applying coating films of chromate of several different thicknesson cold rolled rimmed steel sheets of 0.8 mm thickness and then applying on the surface 0.5 g/m of hexadecanol by hot melting followed by rolling. Results thereof are shown in Table 8.

TABLE 8 Coating film of chromate CCV ErV applied (mg/m) 0 37.5 10.5 20 37.2 10.7 50 36.7 11.9 200 36.4 12.2 500 36.2 12.6 2000 36.5 12.3

As is readily seen in the table, the workability was improved with the increase of the amount of applied chromate coating film, and this inclination becomes remarkable for the amounts exceeding 50 mg/m of the coating film.

EXAMPLE 6 Tests of workability were conducted with the steel sheets of this invention, A through G, which were prepared by applying several different amounts of copper plating on cold rolled rimmed steel sheets of 0.8 mm thickness and further applying on them a toluene solution of hexadecanol to such an extent as to form a layer of non-volatile matter of 0.3 g/m, and with the steel sheets of previous treatment, H and 1. Results are shown in Table 9.

A Steel sheet on which 10 mg/m of copper was plated B: mg/m C1" 250 mg/m D 1 500 mg/m E 2 g/m F 10 g/m G1" 50 g/m 1-1 (Previous treatment) The same material as in C on which commercial press oil was applied. I (Previous Treatment) The same material as in A on which commercial press oil was applied.

TABLE 9 Amount of copper CCV ErV plate (mm) (mm) A 10 mg/m 38.5 10.3 B 100 38.4 10.3 Examples C 250 v 37.4 11.1 of D 500 37.1 11.4 this E 2 g/m 36.4 12.0 invention F 10 36.5 1 1.8 G 50 36.3 11.9 Examples of H 250 mg/m 38.2 10.6 conventional treatment 10 38.8 10.1

A-G: Examples of this invention H and 1: Examples of conventional treatment As is seen in the table, workability was improved with the examples of this invention, C through G, for which the amount of copper plated was larger than 250 mg/m but, as the amount exceeded 2 g/m", the improvement became rather sluggish. In contrast, the workability of the conventional treatment, H and l, was inferior to that of C and A, respectively, in which the same amounts of copper were plated.

What is claimed is:

l. A surface treated steel sheet suitable for use in a forming operation which comprises a steel sheet having thereon a top layer of an alcohol having at least 12 carbon atoms, which alcohol is a solid at room temperature, and interposed between the alcohol layer and the steel sheet, a layer of a metal selected from the group consisting of Zn, Pb, Cu, Cr, Cd, Sn, Al, and alloyed combinations thereof.

2. A surface treated steel sheet suitable for use in a forming operation which comprises a steel sheet having thereon a top layer of an alcohol having at least 12 carbon atoms, which alcohol is a solid at room temperature, and interposed between the alcohol layer and the steel sheet, a layer of a hydrated oxide or a metallic oxide. 

2. A surface treated steel sheet suitable for use in a forming operation which comprises a steel sheet having thereon a top layer of an alcohol having at least 12 carbon atoms, which alcohol is a solid at room temperature, and interposed between the alcohol layer and the steel sheet, a layer of a hydrated oxide or a metallic oxide. 